| A | B |
|---|
| Name | Definition |
| matter | anything that has mass and takes up space |
| atom | a very small particle that makes up the surface of matter |
| nucleus | region located at the center or an atom and contains most of the atom’s mass |
| proton | positively charged particle located in the nucleus |
| neutron | neutral particle, which has no charge, located in the nucleus |
| electron | negatively charged particle that moves in the space surrounding the nucleus |
| mass | a measure of the amount of matter in an object |
| spectral line | a single wavelength of light that can be seen when the light from an excited element is passed through a prism |
| energy levels | regions of space in which electrons can move about the nucleus of an atom |
| electron cloud | a region surrounding an atomic nucleus where an electron is most likely to be found |
| electromagnetic spectrum | the entire range of electromagnetic waves of different wavelengths |
| element | a pure substance made from atoms that all have the same number of protons |
| atomic number | the number of protons an atom has in its nucleus |
| mass number | sum of the number of protons and neutrons in an atom |
| isotopes | one of two or more atoms of an element having the same number or protons in their nuclei, but a different number of neutrons |
| average atomic mass | weighted-average mass of the mixture of an element’s isotopes |
| ion | an atom that is no longer neutral because it has gained or lost electrons |
| periodic table | table of the elements arranged according to repeated changes in properties |
